<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>my css</title>
    <style>
        * {
            margin: 0;      /*外边距*/
            padding: 0;     /*内边距*/
        }
        h1 {
            text-align: center;
        }
        .c1 {
            color: purple;
        }
        p.c2 {
            background-color: gray;
        }
        div .c1 {
            font-style: italic;
        }
        #id1 {
            font-weight: bold;
        }
        .c2, #id1 {
            text-align: right;
        }
        a:link {     /*访问前*/
            text-decoration: none;
        }
        a:visited {   /*访问后*/
            color: gray;
        }
        a:hover {     /*鼠标悬停*/
            font-size: 1.3em;   /*字体大小为原来的1.3倍*/
        }
        .c3 {
            width: 200px;
            height: 400px;
        }
        img {
            width: 100%;   /*占据父元素全部大小*/
            visibility: hidden;   /*隐藏*/
        }
        .c3:hover img {   /*设置鼠标悬停在.c3上img的样式*/
            visibility: visible;   /*可见*/
        }
    </style>
</head>
<body>
<div class="c3">
    <img src="http://pic-bucket.ws.126.net/photo/0003/2020-09-17/FMN8JA1900AJ0003NOS.jpg">
</div>

<h1>达内云计算 cloud computing</h1>
<hr>
<div>
    <a href="http://www.redhat.com" target="_blank">redhat</a>
</div>
<hr>
<div class="c1">达内云计算 cloud computing</div>
<div class="c2">达内云计算 cloud computing</div>
<div>达内云计算 <span class="c1">cloud computing</span></div>
<div id="id1">达内云计算 cloud computing</div>
<div>达内云计算 cloud computing</div>
<p class="c2">达内云计算 cloud computing</p>
<p class="c1">达内云计算 cloud computing</p>
<p>达内云计算 <span class="c1">cloud computing</span></p>
<p>达内云计算 cloud computing</p>
<p>达内云计算 cloud computing</p>
</body>
</html>